Question

Here’s the format of the code:

class C
{
public:
    C();
    virtual ~C() = 0;
};

class D : public C
{
public:
    D();
    ~D();
};

C::C(){
}

C::~C(){
}

D::D(){
}

D::~D(){
}

int main(){
    C *c = new C();
    D *d = new D();
    return 0;
}

When I try to instantiate c I get the following error:

1>c:\main.cpp(59): error C2259: 'C' : cannot instantiate abstract class

I know I cannot call the virtual destructor, but there is something terribly I don’t know on the concepts. Can someone explain me?

Answer 1

You can’t instantiate C because you have explicitly said it’s destructor is undefined.

You could just do:

class C
{
public:
    C();
    virtual ~C() {}
};

instead.

You can leave C exactly “as is” as long as you don’t try to instantiate it (i.e. you only create Ds, but you can pass them around as Cs.